The K40 is a reliable yet inexpensive tire for recreational use. Its grooved tread provides traction without slowing you down on the pavement. This version of the Kenda K40 Tire is available in 24 x 1 38 inch 37-540 ISO a size used on some children’s bikes and many wheelchairs. 55 PSI max. 60 TPI. Wire bead. BlackGumwall. 503g.